A box contains $10$ red balls, $5$ green balls, and $11$ blue balls. If a ball is randomly chosen, what is the probability that it is not blue?
Answer: There are $10 + 5 + 11 = 26$ balls in the box. There are $11$ blue balls. That means $26 - 11 = 15$ are not blue. The probability is $ \frac{15}{26}$.